You can either use grep like this: if (grep {$variable eq $_} qw( ABA SCO ACC PHC GHF )) (where qw builds a list of words).
Or use List::Util's any (with its more intuitive name, and slightly faster since it will stop searching as soon as a match is found):

use List::Util qw( any );
if (any {$variable eq $_} qw( ABA SCO ACC PHC GHF ))
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$a is a special variable, than can be used by sort or some functions of List::Util, that's why I used $variable instead.

And also note that I used eq, which compares two strings, while == compares numbers. Perl will actually complain about this if you have warnings enabled (which you really should, as it lets perl tell you where it thinks you have done a mistake, and it is often right).